Archimedes Texts

129
Iron ones. If Lead is daubed with any Sort
of Filch, it quickly spoils; and for this Reason
we should take Care that our Roof be not a
convenient Harbour for Birds; or if it is a like
ly Place for them to get together in, we should
make our Stuff thick where their Dung is to
fall. Eusebius tells us, that all round the Top
of Solomon's Temple there was a great Number
of Chains, to which hung four hundred little
Bells continually vibrating, the Noise of which
drove away the Birds. In the Covering we
also adorn the Ridge, Gutters and Angles, by
setting up Vases, Balls, Statues, Chariots and
the like, each of which we shall speak of in
particular in its due Place. At present I do
not call to Mind any thing further relating to
this Sort of Ornaments in general, except that
each be adapted to the Place to which it is
most suitable.

That the Ornaments of the Apertures are very pleasing, but are attended with
many and various Difficulties and Inconveniences; that the false Apertures
are of two Sorts, and what is required in each.

The Ornaments of the Aperture give no
small Beauty and Dignity to the Work,
but they are attended with many great Diffi
culties, which cannot be provided against
without a good deal of Skill in the Artificer,
and a considerable Expence. They require very
large Stones, sound, equal, handsome and rare,
which are Things not easily to be got, and
when got not easily removed, polished, or set
up according to your Intention. Cicero says,
that the Architects owned they could not set
up a Column exactly perpendicular, which in
all Apertures is absolutely necessary both with
Respect to Duration and Beauty. There are
other Inconveniencies besides; which, as far as
lies in our Power, we shall endeavour to pro
vide against. An Aperture naturally implies
an Opening; but sometimes behind this Open
ing we run up a Wall which makes a Kind
of false Opening which is not pervious but
closed up; which for this Reason we shall ac
cordingly call a false Aperture. This Sort of
Ornaments, as indeed were most of those
which serve either to strengthen the Work or
to save Expence, was first invented by the
Carpenters, and afterwards imitated by the
Masons, who thereby gave no small Beauty to
their Structures. Any of these Apertures would
be more beautiful if their Ribs were all of one
Piece, made of one entire Stone; and next to
this, is the having the Parts so nicely joined
that the Joints cannot be seen. The Ancients
used to erect their Columns and other Stones
which served as Ribs to these false Apertures,
and fix them firm on their Bases, before they
carried up the Wall; and herein they did very
wisely; for by this Means they had more Room
to use their Engines, and could take the Per
pendicular more exactly. You may plant your
Column perpendicular upon its Base in the fol
lowing Manner: In the Base and at the Top
and Bottom of the Column mark the exact
Center of each Circle. Into the Center of the
Base fasten an iron Pin, soddering it in with
Lead, and make a Hole in the Center of the
Bottom of the Column, just big enough to re
ceive the Pin which sticks up in the Center of
the Base. In the Top of your Engine, or
Scaffolding, make a Mark exactly perpendicu
lar over the Pin which sticks up in the Center
of the Base, which you may find by letting sall
Line from thence to that Pin. When you
have thus prepared every Thing, it will be no
hard Matter to move the Head of the Shaft
till its Center answers exactly to the Mark
which you have made above and is perpendi
cular to the Center of its Base. I have observ
ed from the Works of the Ancients that the
softer Sort of Marble may be smoothed with
the very same Instruments with which we
plane Wood. The Ancients also used to set
up their Stones quite rough, only smoothing
the Heads and Sides of them which were to
join to other Stones, and asterwards when the
Building was raised, they polished the Faces of
the Stones, which they had lest rough before;
and this I believe they did that they might
leave the least Expence that was possible to the
Hazards of their Engines: For it would have
been a much greater Loss to them, if by Acci
dent any Stone that was quite smoothed and
polished had been let fall and broke, than if